import java.util.Scanner;
public class test {
	public static void main(String [] args){
		int i,k=1;
		long add = 0;
		int [] n=new int [args.length];
		for (i=0; i<args.length; i++){
			n[i] = Integer.parseInt(args[i]);
		}
		for (i=1;i<=n[0];i++){
			k*=i;
			add+=k;
		}
		System.out.println(add);
	}
}
